1. Field of the Invention
Embodiments of the invention generally relate to robots suitable for use in semiconductor processing systems.
2. Background of the Invention
The modern semiconductor processing system typically includes a central transfer chamber surrounded by a plurality of processing chambers. The central transfer chamber is generally coupled to a factory interface by one or more load lock chambers suitable for transferring the substrate between the vacuum environment of the transfer chamber and the generally atmospheric environment of the factory interface. The factory interface typically contains one or more substrate storage cassettes for staging processed and unprocessed substrates.
Accurate and repeatable substrate transfer using the robots of the semiconductor processing system is essential to ensure the processing results, to reduce damage to substrates and processing equipment, and to enhance repeatability between substrates.
FIG. 7 depict one embodiment of a typical single-blade substrate transfer robot 700 utilized in many semiconductor processing systems. The robot 700 includes a blade 710 for supporting a substrate 712 during transfer. The blade 710 is coupled to a body 704 by a linkage 702. The linkage comprises a first arm 706 and a second arm 708 that are coupled to the body at a first end and coupled to a wrist 714 at a second end. The wrist is coupled to the blade 710. Each arm 706, 708 is coupled to a respective motor (not shown) concentrically stacked within the body 704. The positioning of the blade 710 is determined by the relative angular positioning of the respective arms 706, 708 by the concentrically stacked motors. For example, if the linkages 706, 708 are rotated by the concentrically stacked motors in the same direction about the central axis 720 of the body 704, the blade 710 is rotated about the central axis 720 as shown by the arrow 716. If the first arm and second arm 706, 708 are rotated in opposite directions, the blade 710 is radially extended or retracted, as shown by arrow 718.
However, the ability to accurately position the blade 710 may be compromised by a number of factors. For example, the linkage 702 and/or the blade 710 may become bent during handling or maintenance procedures. Additionally, thermal expansion of the linkage or loosening of the belts commonly used within the linkage may result in positional drift of the blade. Thus, the blade may not arrive in the position expected based on a calculated movement of the arm. As these aforementioned problems undesirably diminish the ability for efficient and repeatable substrate transfer, it would be desirable to improve the positional accuracy of the robot blade.
Therefore, there is a need for a method and apparatus for monitoring the position of a substrate transfer robot.